What are the four pins on the HEGO (heated oxygen sensor) connector?

The diagram labels the four pins as +12 VOLTS, GROUND, SIG RTN (signal return), and HEGO (sensor signal).

Which pin carries the oxygen sensor signal?

The pin labeled HEGO, shown at the lower right of the connector face view, is the sensor signal output.

Where is the +12 volt heater power pin on the HEGO connector?

The +12 VOLTS pin is shown at the upper left of the connector in the face view, opposite the GROUND pin on the upper right.

Does the diagram show wire colors for the HEGO connector?

No, the diagram only labels pin functions (+12 VOLTS, GROUND, SIG RTN, HEGO); no wire colors are shown.

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Ford HEGO Heated Oxygen Sensor Connector Pinout Diagram - 1990 Bronco EFI

Heated exhaust gas oxygen sensor connector pinout showing +12 volts, ground, signal return, and HEGO terminals

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HEGO sensor connector pinout diagram labeling the +12 volts, ground, signal return, and HEGO signal terminals.

AI caption May 2011 · Photo 725 of 1799

This document is a simple connector pinout diagram for a Heated Exhaust Gas Oxygen (HEGO) sensor, uploaded as reference material for a 1990 Ford Bronco. The illustration shows a face view of the round 4-pin HEGO sensor connector with each terminal labeled by function. The top-left pin is labeled +12 VOLTS (power for the sensor heater), the top-right pin is GROUND, the bottom-left pin is SIG RTN (signal return), and the bottom-right pin is HEGO (the oxygen sensor signal output). No wire colors, part numbers, torque values, or vehicle applicability information is printed on the diagram itself. A reader can use this diagram to identify which terminal in the harness or sensor connector corresponds to heater power, heater/sensor ground, signal return, and the HEGO signal — useful when testing the sensor with a multimeter, diagnosing oxygen sensor circuit codes, or repairing/repinning the connector. It is part of a larger album of Ford EEC-IV EFI reference diagrams (MAF, ECT, EEC-IV connector, speed density schematics) filed with the owner's 1990 Ford Bronco documentation.

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Frequently asked questions

What are the four pins on the HEGO (heated oxygen sensor) connector?: The diagram labels the four pins as +12 VOLTS, GROUND, SIG RTN (signal return), and HEGO (sensor signal).
Which pin carries the oxygen sensor signal?: The pin labeled HEGO, shown at the lower right of the connector face view, is the sensor signal output.
Where is the +12 volt heater power pin on the HEGO connector?: The +12 VOLTS pin is shown at the upper left of the connector in the face view, opposite the GROUND pin on the upper right.
Does the diagram show wire colors for the HEGO connector?: No, the diagram only labels pin functions (+12 VOLTS, GROUND, SIG RTN, HEGO); no wire colors are shown.